Nonfibrous cellulosic structure and method of producing same



Patented Jan. 3, 1939 I v I a UNITED STATES PATENT OFFICE- NONFIBROUS CELLULOSIC STRUCTURE AND METHOD OF PRODUCING SAME Martin Eli Cupery, Wilmington, DeL, assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application July 21, 1937, Serial No. 154,861. Renewed May 17, 1938 13 Claims. (CI. 91-68) This invention relates to the production of nonto remove excess solution and was then dried. fibrous, cellulosic structures. More particularly, The dry, treated fabric retained about 12% by it relates to the production of non-fibrous celluweight of ammonium sulfamate based on the losic structures containing certain specific flameoriginal weight of the fabric. When the treated proofing and softening agents. crepe fabric was brought into contact with a 6 The present application is a continuation in flame, it did not ignite and it showed no tendency part of my copending application, Serial No. to propagate a flame. An untreated sample 132,617, filed March 23, 1937. readily burned when ignited. I

It is an object of this invention to provide non- When samples of the same cloth were simi- 10 fibrous, cellulosic structures, such as thread, filalarly impregnated with salts of sulfamic acid 10 ments, films, fabrics, caps and bands, and sponges other than the ammonium salt, for example, the containing highly desirable flame-proofing and trimethylamine, pyridine, zinc, aluminum and softening agents. ethylenediamine (disulfamate) salts, the treated It is another object of this invention to provide samples likewise showed a lower rate of combusl5 a method for the production of highly desirable tion. Such treated samples contained from 11 16 flame-proof and softened non-fibrous, cellulosic to 13% of the sulfamate. The ammonium sulfastructures. mate and ethylenediamine disulfamate were more Other objects of the invention will appear hereeffective as fire-retardants than the trimethylinafter. amine salt and the pyridine salt, and, of the metal 20 The objects of the invention may be accomsalts, the aluminum, sodium and calcium salts 20 plished, in general, by incorporating on or inwere more eflectlve than the zinc salt. non-fibrous, cellulosic structures, or adding to Example H the materials from which said structures are I made, sulfamic acid or certain of its salts, as will A sheet of gel r e rat d ll s w passed be described in greater detail hereinbelow. h h a 6% aq ous solution of ammonium 25 A generally satisfactory method of carrying out sulfamate, the excess solution removed by rolls, the invention comprises the wetting or impregd the Sheet then dried on a Series Of drying nating of the non-fibrous, cellulosic structure to lls- (Th expression sheet of gel r at d be treated with an aqueous solution or dispersion llu s r e n at d e ul s s tin n so of the sulfamic acid or salt thereof, of suitable gel f here h r f r nce o a heet of cellustrength, and drying the same, Non-fibrou lose which has been regenerated in the manner cellulosic structures thus impregnated or covered Well knOWIl in the art from a Solution Ce ulos show a decreased tendency to ignite and burn, xanthate (viscose), washed and purified, but not and/or a decreased rate of burning. Many of dried. Regenerated cellulose sheeting in gel form such structures will not propagate a flame u d r may likewise be obtained from solutions of other 35- conditions whereby untreated structures a suitable cellulose derivatives, e. g., cuprammonium readily destroyed by fire, The flame-proofing solutions.) The dried cellulose sheet thus preagents of the present invention have furtherpared Contained about by Weight of ammore been found to be valuable softening agents monlum Sulfamate- The Sheet was soft. fl

4 for non-fibrous, cellulosic structures and may be clear and transparent d w d n c ystallizaused in part or in whole as a substitute for pretion of ammonium sulfamate even under condiviously known softening agents such as, for extions of low temperature and/or low humidity. ample, glycerol, ethylene glycol, foramide, car- When brought into contact withafiame, the sheet bamide and the like. showed excellent flame-proof properties. Under The following examples illustrate methods for no conditions could the sheet, 01' a. bundle of thin 45 practicing the invention, it being understood that strips c f m Such he be made to prop ate the invention is not to be limited by the details set a flame. The sheet was charred only at the point forth therein. of contact with the fiame showing little or no Example I afterflow when the flame was removed. a Similar sheets prepared as described above but A m dium W h cr pe fabric made from vlswith addition of glycerol to the ammonium sulfaeose rayon yarn was immersed in an aqueous mate bath, so that the final product contained solution containing 10% by weight of the amabout 5% glycerol and 18% by weight ammonium monium salt of sulfamlc acid. The cloth was sulfamate, were equally flame-resistant. 56 next passed through tightly fitted rubber rollers Sheets of gel regenerated cellulose which had been treated with 5% aqueous solutions of ordinary flre-retardants such as ammonium phosphate and ammonium sulfate and dried showed undesirable crystallization of such salts in the fllm so that the sheet became opaque and had a very rough crystalline surface. Also, these sheets were considerably more brittle than untreated sheets or sheets containing ammonium sulfamate.

Example III Regenerated cellulose-sheeting in the gel form was immersed in a 10% solution of ethylenediamine disulfamate for one minute, removed, and dried on a frame for 10 minutes at 100 C. After cooling, the cellulose sheet was soft. flexible, clear I lulose was similarly impregnated with unneu-' tralized sulfamic acid and the product likewise showed definite fire-retardant properties compared to the untreated product.

As has been stated above, sulfamates have a softening as well as a fire-retarding action on regenerated cellulose, as is illustrated by the results given in the following table:

-' Tensile Elongation Agent at break strg gg at Percent Liza/sq in. None 11-13 ,400 14,000 17 13,000 Ammonium sulfamate 16 10, 000

The samples used in the above tests (except the control) were prepared by immersing the regenerated cellulose sheeting in 4% aqueous solutionsv of the sulfamates for one minute, re-

moving and drying them at 100 C. for 13 minutes.

and conditioning them at 25 C. and 50% rela= tive humidity for 24 hours. The measurements were made on the standard Scott machine. The control was identical in source and preparation with the other samples except that it contained no sulfamate. The higher elongation and lower tensile strength at break in the case of the samples containing sulfamates indicates the latter exert a plasticizing action. Similar effects in the case of paper and textiles can be recognlzed by one skilled in the art.

Example IV A velvet fabric of woven sill: with a rayon (regenerated cellulose) pile was brought into contact with an 8% aqueous solution of am-v monium sulfamate in such manner that only the back-side of the fabric was moistened while the rayon pile surface was not wetted. After drying, the weight of the treated fabric had increased about 15% of its original weight owing to the ammonium sulfamate which had been absorbed. The dry fabric showed no visible crystallization of ammonium sulfamate and showed no tendency to dust or crock (a common result with ordinary fire-retardants on pile fabrics). Moreover, the fabric showed no increased harshness in handle or feel while the luster, gloss, and general appearance was improved by the above treatment. When brought into contact with a flame, the treated velvet fabric was dimcult to ignite and would not propagate a flame, while the untreated fabric was easily ignited and burned rapidly.

Example V Regenerated cellulose sheeting in the gel form was immersed in a 15% solution of monoethanolamine sulfamate for one minute, removed, and dried on a frame for 10 minutes at 100 C. After cooling, the cellulose sheet was very soft, flexible, clear and transparent, and showed very good fire-retardant properties.

Of the various salts of sulfamic acid, I have found the ammonium salt to be most effective as a fire-retardant. f the salts of organic bases, such as amines, only those in which the ratio of carbon atoms to nitrogen atoms is less than about 3:1 are effective, this probably being due to excessive heat of combustion derived from the bumlng of large organic carbon residues, which tends to nullify the effect of the protective incombustible gases (ammonia and/or nitrogen) which are apparently formed. However, regardless of theaccuracy of this theory, the above generalization is indicated as approximately correct from tests with a variety of sulfamates. Thus, ammonium sulfamate, which has no carbon and two nitrogens, is most effective. Monomethylamine sulfamate and ethylenediamine disulfamate, which have a carbon-nitrogen ratio of 1:2, are excellent fire-retardants though not quite so efiective as ammonium sulfamate. Trimethylamine sulfamate having a carbon-nitrogen ratio of 3:2 is only moderately effective as arethe dimethylamine, the monoethanolamine, and ethylamine sulfamates, whose ratio is 1:1. Pyridine sulfamate, wherein the carbon-nitrogen ratio is :2, is a relatively poor fire-retardant and anilin sulfamate, of ratio 3:1, while effective to some extent, especially in higher concentration, is less effective than would ordinarily be desired for commercial use. The above statements are made of course on the basis of comparable quantities of sulfamate and it should be made clear that in the majority of cases excellent results may be obtained with the lesser effective sulfamates if they are employed in sufficiently large amounts.

In the case of salts from sulfamic acid and inorganic bases (i. e. metallic salts), only those having a metallic content of less than about 52% by weight of the anhydrous salt have any detectable effect. This may be due to the relatively lower amount of non-combustible gases capable of liberation by the very heavy metal sulfamate molecule, but, regardless of the explanation, the generalization appears, on the basis of tests I have carried out with several metallic sulfamates, to be a correct approximation. Thus aluminum sulfamate of 8.6% metallic content, is a very good fire-retardant whereas anhydrous zinc sulfamate of metallic content 25.4% is only moderately effective on an equal weight basis though in large amounts it approaches the aluminum salt in eifectiveness. At the lower end of the scale, lead sulfamate of metallic content 51.9% has only a slight fire-retarding action. The sodium, potassium, calcium, magnesium, cobalt, nickel, manganese, and calcium salts all impart flame-resisauaiio tance to a degree proportionate to the non-metal out th conclusion that the metallic content of the sulfamate should be less than 52% if the' sulfamate is to have any detectable effect and less than about 26% if it is to have any very important effect. Conversely, the nonmetallic content (including sulfur) should be at least 48% and preferably at. least 74%.

Many of the sulfamic acid salts, such as zinc sulfarnate, readily absorb water of crystallization. The hydrated salts may be used if desired in the present invention.

Sulfamic acid itself may also be used as a fireretardant and its effectiveness is only slightly less than the ammonium salt. However, the use of sulfamic acid in many instances is not desirable because of, its acidity and the corresponding deterioration effects which may result from such acidity. The salts of sulfamic acid are practically neutral and therefore more practical when 'an acid reaction is not desirable.

Salts of sulfamic acids in which a hydrogen atom of the NH: group is replaced y a hydrocarbon radical, such as ammonium salts of N- methyl and N-isobutyl sulfamic acids, are effective as fire-retardants, as are salts of iminodi- I sulfamic acid such as diammoniumiminodisulfonate (NH4SO3NHSO3NH4) The compounds with which the present invention is concerned are all included by the comprehensive formula (R-NHSO3) 1R in which R is preferably hydrogen but may be a hydrocarbon radical or the radical NH4S03-, and R. is a cation of valence 1:, which compound has less than three carbon atoms for each nitrogen atom and a non-metallic content of at least 48%.

In the practice of the present invention, the sulfamic acid or salt thereof may be employed in conjunction with ordinary fire-retardants such as ammonium phosphates, ammonium sulfate. boric acid, borax, ammonium carbonate, and ammonium halides with results and advantages proportionate to the relative amount of sulfamlc acid or sulfamate employed.

The concentration of impregnated fire-retardant which is necessary will vary with the effectiveness of the retardant, the degree of fire-retardance desired, and the relative combustibility of the non-fibrous cellulosic material to which applied. In general, materials such as regener ated cellulose or lowly etherified or lowly esterified cellulose derivatives, require from to of their weight of ammonium'sulfamate, or its equivalent, to give products which will not propagate a flame and which ignite with difficulty at the point of contact with the igniting flame. Lower amounts of ammonium sulfamate give less effective protection but" in every case show a decreased rate of burning compared to untreated materials. Lead sulfamate is only slightly effective as a fire-retardant forregenerated cellulose him. On the other hand, the zinc salt is definitely efiective with all these types of materials, and the aluminum salt is highly effective with all of them.

In the examples, the sulfamate is applied from aqueous solution. Fire-retarding effects may also be obtained when the sulfamate is applied by any method. For example, powdered crystals may be dusted upon a damp surface or surface treated with adhesive; the sulfamate may be applied from solution or suspension in an organic liquid; or in the case of a liquid thesulfamate may be incorporated by mixingor milling.

The sulfamates of the amines may be prepared by the reaction of sulfamic acid with the amine preferably in aqueous solution. Metallic salts may beprepared by the methods known in the art, e. g., reaction of a freshly precipltated,.washed,

hydroxide or carbonate of the metal with an aqueous solution of sulfamic acid.

An outstanding advantage of anunonium sul-i -famate and related salts over the more commonly used prior art flame-proofing agents for textile fabrics is the fact that they do not cause the harshness which normallycharacterizes fabrics treated with the prior art fire-retardant or flameprooflng materials and in many instances they have a softening eifect of their own. As flameproofing agents for regenerated cellulose illm, ammonium sulfamate, monoethanolamlne sulfamate and related salts have an advantage over prior art materials in that, even when present in the film in amounts up to about 23%, they do not crystallize out on the surface of the film under ordinary atmospheric conditions (24 C. and 35% relative humidity) as is characteristic of prior art flame-proofing materials. Under favorable conditions, the amount may be as high as without crystallizing out. Furthermore, ammonium sulfamates not only render cellulose and its manufactures (film, thread, fabrics, caps, bands, sponges, etc.) flame-proof, butalso impart to these materials a. certain degree of softness. Hence the sulfamates may also be used, either alone or in conjunction with glycerol or other common softeners, as combined softening and flame-proofing agents. In the case of rayon, the sulfamate may be included in theviscose spinning bath, or it may be applied to the rayon thread or fabric. In the case of cellulose film, the sulfamate may be added with good results to the viscose, to the undried sheet, or to the dried sheet before or after application of moistureproofing lacquers, such as those of Charch and Prindle (U. 8. Patents Nos. 1,737,187 and 1,826,- 696) The fact that the moistureprooflng lacquer may contain highly inflammable substances does not seem to make any appreciable difference. The cellulose thread, fabric, or film which has been impregnated with the sulfamate may be stored for prolonged periods without deterioration by the sulfamates inasmuch as the latter are substantially neutral.

Sulfamic acid and its salts may also be employed as fire-retardants for other non-fibrous cellulosic materials, than regenerated cellulose, for example, cellulose esters such as the nitrate, acetate,-propionate, butyrate, and phthalate and cellulose ethers such as methyl-, ethyl-, benzyl-, crotyl-, hydroxyethylgraded or highly degraded, of any degree of substitution, and of any degree of water-sensitivity. A particular illustration of the flame-proofing of a cellulose derivative is the inclusion of ammonium sulfamate in cellulose nitrate compositions containing pigments and softeners which are to be applied to fabrics; alternatively the sulfamate may be applied to the already coated fabric. 4

'Fabrics that have been treated with sulfamic acid and those of its salts with which this invention is concerned, and thus rendered flre resistant, may be subsequently rubberized and the rubber coating vulcanized under the usual conditions (about 2 to 3 hours at about 120 0.) without appreciable tendering of the fabric.

Sulfamic acid and those of its salts specified and carboxymethylcelv luloses. These cellulose derivatives may be undespirit of the invention is intended to be included within the scope of the claims.

I claim: v

1. A non-fibrous, cellulosic structure containing, as a flame-proofing and softening agent, a compound of the formula (R tin-sown wherein R is hydrogenTa hydrocarbon radical or NHiSOa, R is a cation of valence 1:, said compound having less than three carbon atoms for each nitrogen atom and having a non-metallic content of at least 48%.

2. A non-fibrous, cellulosic structure containing, as a flame-proofing and softening agent, a compound of the formula (NHzSOaMR R being a cation of valence x, which compound has a non-metallic content of at least 48% and.

less than three carbon atoms for each nitrogen atom.

3. A non-fibrous, cellulosic structure containing, as a flame-proofing and softening agent, a salt of sulfamic acid having a non-metallic content of at least 48% and less than three carbon atoms for each nitrogen atom.

4. A non-fibrous, cellulosic structure containing, as a flame-proofing and softening agent, a salt of sulfamic acid having a non-metallic content 'of at least 74% and less than three carbon atoms for each nitrogen atom.

5. A regenerated cellulose structure containing, as a flame-proofing and softening agent, a compound of the formula wherein R is hydrogen, a hydrocarbon radical or NHiSOB, R is a cation of valence 3:, said compound having less than three carbon atoms for each nitrogen atom and having a non-metallic content of at least 48%.

6. A regenerated cellulose structure containing, as a flame-proofing and softening agent, a compound of the formula (NH2SO3):R

R being a cation of valence 2:, which compound has a non-metallic content of at least 48% and less than three carbon atoms for each nitrogen atom.

'7. A regenerated cellulose structure containing,

as a flame-proofing and softening agent, a salt of suliamic acid having a non-metallic content of at least 48% and less than three carbon atoms wherein R is hydrogen, a hydrocarbon radical or N11480:, R is a cation of valence 3, said compound having loss than threecarbon atoms for each nitrogen atom and having a nonmetallic content of at least 48%.

10. In the production of regenerated cellulosic structures, the step which comprises treating the structures with a flame-proofing and softening agent comprising a compound of the formula where R is hydrogen, a hydrocarbon radical or Nil-4803, R is a cation of valence :c, said compound having less than three carbon atoms for each nitrogen atom and having a non-metallic content of at least 48%.

11. In the production of regenerated cellulosic structures, the step which comprises treating the structures with a flame-proofing and softening agent comprising a compound of the formula R being a cation of valence x, which compound has a non-metallic content of at least 48% and less than three carbon atoms for each nitrogen atom.

12. In the production of regenerated cellulosic structures, the step which comprises treating the structures with a flame-proofing and softening agent comprising a salt of sulfamic acid having a non-metallic content of at least 48% and less than three carbon atoms for each nitrogen atom.

13. In the production of regenerated cellulosic structures, the step which comprises impregnating the structures while in the gel state with a flame-proofing and softening agent comprising a compound of the formula wherein R is hydrogen, a hydrocarbon radical or NH4S03, R is a cation of valence 1:, said compound having less than three carbon atoms for each 

